Obsidianby Laura Martin and Amy IsvikObsidian is a type of rock. A rock is a natural substance. It is composed of crystals of different materials that have been fused into a solid lump. Not all the minerals have to be from the same origin or even time of occurrence. They only have to be fused together by natural occurrences. There are three types of rocks, metamorphic, igneous, and sedimentary. Obsidian is an igneous rock. It forms when molten rock material cools so quickly that the molecules do not have time to form into a crystalline structure. Obsidian is normally an extrusive rock, but it can form in a variety of locations so it is not always extrusive. When it forms along the edge of a lava flow, or forms when lava cools while airbourne, or when if forms where lava touches water, then it is extrusive. When it forms, though, as it cools on the edge of a sill or dike, then it is intrusive. Obsidian is most commonly found in the color of black. It can also be brown and green. Very rarely, obsidian can be found in the colors of blue, red, orange, and yellow. Obsidian has a glassy texture and cooled rapidly without time to form crystals so it has no actual grain size. There are no minerals in obsidian because obsidian has no crystals. Obsidian is sometimes classified as a mineraloid, because it lacks the crystal structure needed to be a mineral. Other "mineraloids" are Limonite and Opal. Obsidian is SiO2 with large amounts of impurities.
Obsidian has a vitreous luster. Obsidian is also translucent in any specimen of sufficient size. It's hardness ranges between a 5 and a 5.5 on the Moh's Hardness Scale. It's specific gravity is roughly 2.6, which is rather average. Obsidian has a white streak. The fracture of Obsidian is conchoidal, which causes it to break into pieces with curved edges. These curved edges are very sharp and this is why Obsidian was used for the making of tools and as a tool itself by ancient civilizations. Obsidian can be found in many places of the world, but it is found in areas where there has been recent geographical activity. Obsidian is rarely found older than a few million years old. This is because it is destroyed or altered by processes such as weathering and heat among others. Notable places where obsidian can be found in Argentine, Canada, Ecuador, Chile, Guatemala, Greece, Indonesia, Hungary, Iceland, Scotland, Kenya, Japan, Italy, Mexico, Peru, New Zealand, Russia, the United States, and many other places. In the United States it is not found east of the Mississippi River (so no Obsidian in Iowa!) but it is found in Arizona, Idaho, California, Nevada, Oregon, New Mexico, Texas, Colorado, Washington, and Wyoming. It also occurs in the Cascade Mountains and it's associated lava beds. Most of the Obsidian used in the jewelry trade is found in the United States.
Obsidianby Laura Martin and Amy Isvik Obsidian is a type of rock. A rock is a natural substance. It is composed of crystals of different materials that have been fused into a solid lump. Not all the minerals have to be from the same origin or even time of occurrence. They only have to be fused together by natural occurrences. There are three types of rocks, metamorphic, igneous, and sedimentary. Obsidian is an igneous rock. It forms when molten rock material cools so quickly that the molecules do not have time to form into a crystalline structure. Obsidian is normally an extrusive rock, but it can form in a variety of locations so it is not always extrusive. When it forms along the edge of a lava flow, or forms when lava cools while airbourne, or when if forms where lava touches water, then it is extrusive. When it forms, though, as it cools on the edge of a sill or dike, then it is intrusive. Obsidian is most commonly found in the color of black. It can also be brown and green. Very rarely, obsidian can be found in the colors of blue, red, orange, and yellow. Obsidian has a glassy texture and cooled rapidly without time to form crystals so it has no actual grain size. There are no minerals in obsidian because obsidian has no crystals. Obsidian is sometimes classified as a mineraloid, because it lacks the crystal structure needed to be a mineral. Other "mineraloids" are Limonite and Opal. Obsidian is SiO2 with large amounts of impurities.
Obsidian has a vitreous luster. Obsidian is also translucent in any specimen of sufficient size. It's hardness ranges between a 5 and a 5.5 on the Moh's Hardness Scale. It's specific gravity is roughly 2.6, which is rather average. Obsidian has a white streak. The fracture of Obsidian is conchoidal, which causes it to break into pieces with curved edges. These curved edges are very sharp and this is why Obsidian was used for the making of tools and as a tool itself by ancient civilizations.
Obsidian can be found in many places of the world, but it is found in areas where there has been recent geographical activity. Obsidian is rarely found older than a few million years old. This is because it is destroyed or altered by processes such as weathering and heat among others. Notable places where obsidian can be found in Argentine, Canada, Ecuador, Chile, Guatemala, Greece, Indonesia, Hungary, Iceland, Scotland, Kenya, Japan, Italy, Mexico, Peru, New Zealand, Russia, the United States, and many other places. In the United States it is not found east of the Mississippi River (so no Obsidian in Iowa!) but it is found in Arizona, Idaho, California, Nevada, Oregon, New Mexico, Texas, Colorado, Washington, and Wyoming. It also occurs in the Cascade Mountains and it's associated lava beds. Most of the Obsidian used in the jewelry trade is found in the United States.
Obsidian has many uses. It was once used by Native Americans to make sharp tools for scraping and cutting. Perlite, which is a substance formed by the heating of obsidian, is mixed with soil to start the growth of vegetables seeds. Thin blades of Obsidian are placed in surgical scalpels to provide a sharp edge and help with accuracy. In controlled tests, Obsidian blades faired just as well, or better, than blades made out of surgical steel. Obsidian is often used in the creation of jewelry. As it has a relatively low hardness, it is often used as a media for carvers and other artists.